To disperse the effluent from storm drains and subsurface sewage disposal systems within the earth, use has been made of covered pits ("dry wells ") and perforated pipes set in gravel filled trenches, along with preformed concrete structures having sidewall and bottom holes. Within the last decade, molded plastic arch shaped leaching chambers (also referred to as leaching conduits) sold under the registered U.S. trademark "Infiltrator", have met substantial commercial success. Examples of such type of chambers are shown in U.S. Pat. No. 4,759,661 to May and Nichols; and, in U.S. Pat. Nos. 5,017,041, 5,156,488 and 5,336,017 all to Nichols. All of the foregoing patents have an inventor and assignee in common herewith. The Nichols type of commercial chambers are generally arch shaped, have open bottoms, sidewalls corrugated for strength, and have sloped sidewalls with a multiplicity of slotted perforations. They typically are 190 cm long by 86 cm wide and 30-45 cm high.
Generally, such molded chambers are placed end-to-end in a trench and then covered over with soil. Liquid is piped into the chamber system and passes through the open bottom and perforated sidewalls, into the soil. A biological membrane, also called a biomat, forms in the soil near the perforations, and limits the per unit area flow of liquid into the soil. Thus, high degrees of perforations are desired, to increase the leaching capacity of a chamber. Leaching chambers with high flow rating will desirably require the less trench length, fewer chambers, and thus lower cost.
However, there are several design factors competing with the objective of maximum liquid dispersal. They include: The sidewall must resist vertical and sideways forces. The sidewall openings must limit entry of the surrounding soil into the chamber. The chamber base must provide sufficient bearing area on the underlying soil, to resist the weight of earth and any vehicles passing over the soil above. The chamber design must be straightforward and economic to manufacture. Chambers must efficiently nest each within the other for economic shipment and handling. Further, molded plastic chambers must technically and economically compete with stone filled trenches, pre-cast concrete galleries, and other prior art devices. Thus, designers of chambers have sought to maximize the open area in the peaks and valleys, maximizing the number of openings, and placing the slots as far vertically upward on the sidewalls as possible. But there is still need for better performing chambers.